In most of the commonly known sliding door assemblies, the door simply slides on the slide track. The door is constrained against all other modes of movement apart from sliding along the line of the slide track. In such an arrangement as that it is difficult, as sliding door designers know, to provide an effective weatherseal around the closed door.
For high quality patio doors, therefore, an alternative to this "straight slide" arrangement has been developed, and the alternative has come to be known as the INLINE (trade mark) arrangement.
In the INLINE arrangement, the fixed door frame is provided with a recess. When the moving door is being moved to the closed position, the door enters this recess in a direction which is substantially perpendicular to the line of the slide track. The door has to move bodily forwardly relative to the slide track in order to enter the recess.
In the INLINE arrangement, the door does not rest directly on the slide track; instead, a pair of trolleys rest directly on the slide track and a pair of crank arms link the trolleys to the door. The arrangement is such that when the crank arms pivot, the door undergoes the required lateral movement, and the door enters the recess.